1. Field of the Invention
The present invention relates to an optical recording medium, and more particularly, to an optical recording medium having wobbles formed on at least one lateral surface of grooves of a user data area and grooves of a lead-out area, and configured such that wobble characteristics between the user data area and the lead-out area are different from each other.
2. Description of the Related Art
In general, optical recording media are widely employed as information recording media for an optical pickup device recording/reproducing information on/from the optical recording media. The optical recording media are classified into read-only-memory (ROM) compact discs (CDs) and digital versatile discs (DVDs) according to information recording capacity. Further, a DVD disc which information is written on, erased, and read from, can be sub-divided into a digital versatile disc-random access memory (DVD-RAM) disc and a digital versatile disc-rewritable (DVD-RW) disc.
In a DVD-RAM or DVD-RW disc shown in FIG. 1, there is a lead-in area 10 in which read only data, such as a disc size, the number of track layers on a readable plane, or illegal copy preventing information, is recorded, a user data area 20 in which user data can be repeatedly read and/or written, and a lead-out area 30 in which other disc-related information is recorded.
As indicated by a portion “C” of FIG. 1, there are grooves 23 and lands 25 alternatively formed in the user data area 20 so as for the optical pickup device to perform recording and/or reproducing information marks 27 along a predetermined track. In FIG. 1, reference numeral 40 denotes a reproduction beam. From enlarged portions A and B of the lead-in area 10 and the lead-out area 30, it is confirmed that physical pits 15, which are the read only data, are formed thereon. Here, the lead-out area 30 is used for performing various functions. For example, the lead-out area 30 guards an optical pickup not to deviate from the user data area 20 while the optical pickup performs a recording/reproducing process.
In particular, as shown in FIG. 2, in a dual-layer optical recording medium having a first recording layer L0 and a second recording layer L1 of opposite track paths, the lead-out area 30 allows the optical pickup device to keep performing tracking during interlayer-jumping from an outermost circumference of the first recording layer L0 to another outermost circumference of the second recording layer L1 without deviating from the track paths. The opposite track paths are sequentially addressed from an inner circumference of the first recording layer L0 to an outer circumference thereof, and then from an outer circumference of the second recording layer L1 to an inner circumference thereof.
In a dual-layer optical recording medium, such as a ROM disc, an area serving as the lead-out area 30 varies according to a reproduction method of the second recording layer 12. In the dual-layer ROM disc having the opposite track paths, a middle area is separately provided at each of the outer circumferences of the first and second recording layers L0 and L1. However, in a case of a rewritable optical recording medium, both pits and grooves can be used. Therefore, in a case of dual layer rewritable optical recording media, a recording power is affected by a physical geometry of the first recording layer L0 during recording data. In other words, when recording is performed on the second recording layer L1, a recording light beam passes through the first recording layer L0, resulting in a difference in transmittance between pit portions and groove portions.
Light power was measured for an optical recording medium at a mirror area, a pit area, a groove area and a groove area with marks to simulate the light power depending on a difference in the transmittance according to various conditions of the first recording layer L0, as shown in FIGS. 3A through 3D. Here, the number of tracks trapped by a laser beam transmitted through a lens was taken into consideration.
Tables 1 and 2 list input parameters and items for experimentation. In Table 1, Rc represents reflectivity of a crystallized portion of a recording layer and Ra represents the reflectivity of an amorphous portion of the recording layer.
TABLE 1ParameterConditionWavelength (nm)400Numerical Aperture (NA)0.65/0.85Minimum mark length (μm)0.275/0.194ModulationEFM+ (Eight-to-Fourteen Modulation-plus)Track pitch (TP) (μm)0.30, 0.34, 0.38Reflectivity (%)Rc = 25, Ra = 5
TABLE 2ItemFactorExampleDual recording layerStructure of firstMirror, pits, grooves,recording layergrooves with marks.High NANumber of tracks trapped85 for 0.65 of NAby laser beam160 for 0.85 of NAIncident angle of beam40.5° for 0.65 of NA58.2° for 0.85 of NA
FIG. 4 is a graph showing measurement results of the light power depending on the transmittance for the cases shown in FIGS. 3A, 3B, 3C and 3D. With reference to FIG. 4, according to a simulation result, a decrease in the light power is smallest in the mirror portion (graph line with solid squares), and the light power gradually decreases more in the order of a pit portion (graph line with solid diamonds), a groove portion (graph line with solid triangles) and a groove mark portion (graph line with solid circles). Therefore, as shown in FIG. 4, in the case of a dual layer disc, the transmittance varies according to the physical geometry of the first recording layer L0 while a rewritable optical recording medium can further affect the recording power during recording data. Accordingly, it is necessary to unify the physical geometry of the recording layer and to newly define the lead-out area or the middle area on such an optical recording medium.